Scientific Name and Authority

Botryllus schlosseri   (Pallas, 1766)


Botryllus schlosseri is a colonial tunicate that can form colonies as large as 25 mm x 150 mm and up to 2 mm thick. Color is highly variable within and among colonies, and can be yellow, dark purple, red, brown or black. Colonies consist of many radial clusters of 5-20 zooids forming star-shaped systems. Individual zooids can be 1.75 mm - 5 mm long. There are 12-16 oral tentacles around the oral siphon and 7-9 stigmatal rows. The stomach has 8-10 folds and is somewhat spirally deflected with a prominent pyloric caecum. On each side of peribranchial cavity are 1-4 ovaries which are located above prominent testis. Tailed larvae, about 400 µm long, with eight ampullae, may be present in the cavity (Van Name 1945; Nishikawa 1991; Lambert and Lambert 1998).

A recent genetic analysis indicates 'Botryllus schlosseri' is probably a complex of cryptic species. Five clades (A-E) were identified in Europe, but only one of these (A) was found at sites in the Northwest Atlantic and Northeast Pacific. The other clades had restricted distributions on the coasts of Europe (Bock et al. 2012). However, Yund et al. (2015) have found that clade A is comprised of several subclades, at least one (BS2) of which is native to the Northwest Atlantic.

Taxonomic Classification:

Kingdom: Animalia
Phylum: Chordata
Subphylum: Tunicata
Class: Ascidiacea
Order: Stolidobranchia
Family: Styelidae
Genus: Botryllus
Species: schlosseri


Alcyonium borlasii (Turton, 1814)

Alcyonium schlosseri (Pallas, 1766)

Aplidium verrucosum (Dalyell, 1839)

Botryllus aurolineatus (Giard, 1872)

Botryllus badius (Alder & Hancock, 1912)

Botryllus bivittatus (Milne-Edwards, 1841)

Botryllus calendula (Giard, 1872)

Botryllus calyculatus (Alder & Hancock, 1912)

Botryllus castaneus (Alder & Hancock, 1848)

Botryllus gemmeus (Savigny, 1816)

Botryllus gouldii (Verrill, 1871)

Botryllus marionis (Giard, 1872)

Botryllus miniatus (Alder & Hancock, 1912)

Botryllus minutus (Savigny, 1816)

Botryllus namei (Hartmeyer and Michaelsen, 1928)

Botryllus polycyclus (Savigny, 1816)

Botryllus pruinosus (Giard, 1872)

Botryllus rubens (Alder and Hancock, 1848)

Botryllus rubigo (Giard, 1872)

Botryllus smaragdus (Milne-Edwards, 1841)

Botryllus stellatus (Gaertner, 1774)

Botryllus violaceus (Milne-Edwards, 1841)

Botryllus violatinctus (Hartmeyer, 1909)

Botryllus virescens (Alder and Hancock, 1848)

Botryllus morio (Giard, 1873)

Potentially Misidentified Species:

Botrylloides diegensis

possibly native to northeast Pacific

Botrylloides nigrum
Botrylloides violaceus

northwest Pacific species, widely introduced

Botryllus planus